The present invention relates to variable pitch aircraft propellers of the general type disclosed in U.S. Pat. No. 3,115,937, No. 3,380,535, No. 3,575,529, No. 4,097,189 and No. 4,407,635 assigned to the assignee of the present invention. These propellers usually incorporate a control mechanism for changing the pitch of the propeller blades between a feather position and a reverse position through high and low pitch positions. More specifically, the variable pitch aircraft propeller includes a hydraulic actuating cylinder assembly which mounts on and rotates with the hub of the propeller and receives hydraulic fluid from a governor unit driven by the aircraft engine. The governor unit preferably incorporates a positive displacement hydraulic pump which supplies hydraulic fluid through a governor control valve actuated by flyball weights responsive to the speed of the engine shaft. The governor control valve operates to maintain the engine speed substantially constant by precisely controlling the pitch of the propeller blades, but can be manually adjusted to change the blade pitch during flight.
As disclosed in above-mentioned U.S. Pat. No. 3,115,937, the hub assembly and hydraulic pitch changing cylinder assembly is commonly enclosed by a spinner assembly including an annular spinner bulkhead formed of aluminum sheet metal and mounted on the rearward portion of the hub. The bulkhead supports a dome-shaped cover or spinner dome which is removably secured to the bulkhead by peripherally spaced fasteners or screws. Usually, the dome of the spinner assembly is formed by spinning a circular sheet of aluminum. More recently, the spinner dome has been molded of high modulus fibers impregnated with epoxy resin and heat cured within a mold to provide a dome having substantial strength but significantly lighter than the aluminum sheet metal dome.
It is also common to provide the aircraft propeller assembly with a de-icing system. This system usually incorporates rubber covered electrical heating elements which are bonded by cement to the leading edge portions of the blades. Electrical power is supplied to the elements through a slip ring assembly including concentric copper rings retained within an annular insulating block for receiving corresponding carbon brushes. The block is recessed within an aluminum mounting ring which is secured by fasteners to the propeller hub adjacent the rear surface of the aluminum sheet metal bulkhead. Separate terminal blocks are mounted on the hub portions of the blades, and electrical wires extend from the copper rings through holes within the aluminum bulkhead for connecting the slip rings to the terminal blocks which also receive conductor wires extending from the heating elements. This slip ring assembly is relatively heavy and complex in construction and requires substantial time for assembly and servicing.